28-38-48 swapped to 22-32-42 - FD shift problems

[howfar]

To get lower gearing on my tourer I've swapped the Alivio 28-38-48 crankset for a 22-32-42 set. It's square taper and I run an 8 speed 11-32 cassette at the rear.

When climbing the shift from the middle to granny ring won't drop the chain.On the level it drops OK. I've got the derailler at the right height and I have non-indexed bar end shifting. I've swapped the mech for a new one and removed the spokes from the chainstay holders to get the right height so the end of the cage is unimpeded. The front derailler is a Sora FD-2303. If the FD is mounted to high the Middle to Large change is affected.

To get the chain to drop I have to dismount and lift the back wheel and turn the cranks by hand and it drops straightway like it does on level roads.

The bike is a Raleigh Randonneur in a 25" frame and I'm 16 stone (100kg).
Is the frame twisting so as to cause a problem?
Would a longer bottom bracket axle give a better contact with the FD cage?
Would an MTB FD be more appropriate?

I had no problems with the old cranks - any thoughts on what I can do to sort it out before I shell out on the wrong new bits!

[CREPELLO]

Have you let out the inner stop screw all the way?
As you have bar end shifters you can swap for the most ideal FD - MTB, but go for a conventional swing; they're much better IMO. I have run a conventional LX FD with a 107mm BB and bar ends.

Alternatively, as you say, a longer BB may work, but it may mess up chainline. I think I'd be inclined to go for the MTB mech.

[howfar]

The stop screws allow the mech to go all the way towards the frame - it swings back to it's max extent.

I have an old 118mm UN54 BB in my box of bits in the garage so will try that when get time - if no luck I'll take the Deore FD of my commuter and see if there's any change! Oh the joys of fettling!

[andrew_s]

You did remember to move the front mech down the seat tube?

The front mech cage, as it's a road front mech, is curved for a large chainring with a minimum of 48T. If you use it with smaller chainrings, there will be more chain between the point the mech is pushing the chain and where it contacts the chainring, and therefore more scope for the chain to just flex rather than derail.

An MTB front mech has a more curved cage suitable for the smaller chainrings. However many have a minimum difference between middle and outer of 12T or thereabouts, so when used with the mech set just abouve the outer chainring as normal, the inner cage plate fouls the middle ring when trying to change to outer. You therefore have to mount the front mech higher up the seatstay than ideal.

All part of the joy of trying to use components highly optimised for one set of gear ratios on something different that suits you

[cycleruk]

The 22/32/42 is an MTB chainset so really should be using an MTB front mech'. (as you are using friction shift there should not be a problem with the extra cable pull required)
The Sora is a road mech' and as Andrew_S says is not the ideal.
You could try angling the rear of the dérailleur in a bit so that it contacts the chain sooner.)

[Brucey]

worth taking a look at the chainline, too. It could be that the mech travel simply isn't enough for a different chainline.

BTW if it is an 8s chainset and you are running a 9s chain that can sometimes cause problems. Sometimes a different chain or a different front mech will mysteriously solve a problem like this, and (slightly annoyingly) it isn't easy to see what the difference really is.

cheers

[markfh]

Just to add to Brucey's comment on chainline. The 8-speed Alivio chainsets are specified for a 50mm chain line in the corresponding Shimano techdoc (http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Alivio-Acera/SI_0094A/SI-0094A-001-ENG_v1_m56577569830667768.PDF). An additional complication is that although there appears to be three variants of the 8-speed Alivio chainset for square taper BBs with 48/38/28 chainrings (FC-M411/M361/M311) there are four variants with 42/32/22 chainrings (FC-M411/M361/M311 and FC-M410) and the FC-M410 requires different a different BB spindle length to achieve the specified 50mm chainline (see the table "Bottom Bracket" in the Shimano techdoc). I have assumed that you are using a 8-speed Alivio chainset as the corresponding document for a 9-speed Alivio does not include a 48/38/28 variant. Note I am not saying that you have to use a 50mm chainline only that if you have changed from a FC-M411/M361/M31 to a FC-M410 and not done a corresponding change to your BB spindle/axle length you may have inadvertently changed your chainline.

[howfar]

Back from the garden centre now!

The chainline measured at 44mm - the FD tech docs stated 45mm (Sora FD 2303)

The Alivio stuff is all 8 speed and I'm using an 8 speed chain. Just assumed the throw on a triple needed the right chainline regardless of cranks especially if not indexed.

I can't remember what length BB I put in originally - UN54's seem to last years.

I've an inkling it's 113mm so my 118mm spare will only give me half the required extra oomph to get a 50mm chainline - the seat tube is good old 28.6mm not 31.8/34.1mm. A 122mm BB seems extreme!

Will get the 118mm in this evening hoping a 47.5mm chainline suffices. Still seem to use the middle chainring most even with the reduced tooth count.

Thanks for the pointers everyone. Will let you know how I fair.

[Brucey]

in which case I don't think you need the wider chainline for the mech you have at present... and I'm still confused about why you are having troubles.

With the Sora mech, I'm not sure that the wider chainline will really help. However if you can only get an MTB mech to match the chainring sizes well, it may be that you can't run it at a narrow chainline. I'd still try first though, and as someone else mentioned, I'd try and get an MTB mech with a bottom swing if I could since this will usually run a tighter chainline better than a top swing mech.

cheers

[howfar]

It was a 113mm BB and the 118mm went in easily - glad I greased everything years ago!

The mech high low screws have been set for the new chainline and the mech positioned as low as it will go without hitting the top of the chainstay and the remaining spoke - the outer profile of the chain cage contacts the chain well on the majority of sprockets.

Tested on the flat and the 4 largest sprockets under load are OK - smaller than that and there's a bit of clatter and oscillation of the mech when I look done before it drops.

Have to wait for a big hill tomorrow to see if there is any real improvement.

My gut feeling is I'll need an MTB mech - the current chainline doesn't look right.

I wanted to get sub 20" gear inches but it seems I'm causing myself more trouble than necessary.

[cycleruk]

Would you need to shorten the chain as you have smaller chainrings?
Don't know if it would make any difference though.

[531colin]

if you get an MTB front mech, go for conventional swing, but get an oversize one and an eccentric shim like this..http://www.sjscycles.co.uk/thorn-eccentric-front-mech-shim-286-to-349-black-plastic-hand-finished-split-prod6448/....so you can adjust the MTB front mech to your nice tight chainline.
A jump stop/chain watcher thing is also useful, it means you can set the mech limit so that it shifts every time, and the jump stop prevents over-shifting and the chain dropping on the BB.

[howfar]

Test ridden this morning up a steep hill - small order of success with the chain slipping slipping off the middle chainring to the small chainring when using the 3 largest sprockets at the back and having to really lighten the pressure on the pedals with the 2 sprockets below that but still not shifting with the 3 smallest sprockets.

The new 118mm BB has had an effect and the low stop screw on the FD is set all out so the FD cage goes back all the way without the chain unshipping. I'm used to the chain unshipping with all combinations of chainring/sprocket

Chainline bias has moved towards the high gears - it looks OKish on the 5 highest (small) sprockets on the large chain ring but to my eye only the 3 lowest (larger) sprockets at the back on the small chainring - middle chainring all still seems fine.

Looks like I'll be experimenting with an MTB mech from my commuter as I don't want an extreme chainline. It's a bottom clamp Deore dual pull. (FD-M591)

Thanks for the pointer to the tech docs - it seems a 123/126mm BB is recommeneded but I won't go down that route due to chainwear. The drop outs at the back of the bike are still 126mm OLN so compared to a modern 135mm OLN bike the chainline issue has another 4.5mm factor.

Most hills are easily doable using just the middle chainring but with panniers the granny ring has to be there reliably for me when needed.

I'm not 100% sure a more traditional crankset like a Stronglight or Spa in say 24-32-42 using my 113mm BB and Sora mech sort my problems out - dispensing with the Alivio MTB which worked well in 28-38-48 but not in 22-32-42 - or just try a larger granny ring in 24 or 26 teeth giving 20" and 22" lowest gear - last option would be much cheaper even buying both sizes!

[markfh]

Just a thought, would it be possible to swap the 22 ring from your new crankset to your original crankset. As far as I can see the problem is that the chain will not "fall-off" the 32 middle ring when you try to change down but it worked OK when you had a 38 middle ring. This will give a rather large drop when changing from middle to inner but it might be worth trying although there is a risk that the chain may rub on the bottom of the cage as you will have to raise the front dérailleur to its original position. It would be as well to see how much gap there is under the chain when you are running small to small before trying noting that in reality you will probably try to avoid this.

What was the chainline measurement in your original configuration and have you measured the chainline of your new configuration? The reason for asking is that when referencing the Shimano techdocs I did try to indicate that you did not necessarily have to use a 50 mm chainline which is Shimano's normal specification for a triple on a MTB whereas their specification for a road bike triple is 45mm. I have used a Spa Cycles XD2 triple on an old touring frame with a 68mm wide shell last year with a Shimano UN55 107 mm BB and achieved a chain-line of 45 mm (as intended). I cannot remember why I specifically chose a 107 mm Shimano UN55 rather than a 110mm one (the Spa website suggests a "110mm JIS square taper bottom bracket. eg Stronglight JP400" but does not say what chain-line they are trying to achieve) other than the fact that at the time Spa were out of stock of Aluminium JP400s. I do remember deliberating over it for a while and then being pleasantly surprised when the chain-line worked out as intended. I was also working with a 126 OLN rear wheel with a 6 speed Suntour ultra freewheel at the time hence the desire for a 45 mm chainline.

I also remember that I initially tried the Spa XD2 (48/38/23) with the original Suntour (double) front dérailleur and had similar problems to what you describe in that it would not reliably shift to the inner ring. Watching what happened when I tried to shift it was clear that when under load the tension in the chain was more than the dérailleur spring could deal with - when I lightened the pressure on the cranks the cage would move in and when I put more load on the cranks the cage would move out- all with no movement of the (friction) shifter. The original crankset had IIRC a 52 outer so like you the curve of the dérailleur cage no longer matched the curve of the outer so there was quite a distance along the chain from the middle ring to where the chain rubbed against the dérailleur cage when trying to change. In the end I changed to more modern (& triple) front dérailleur and that overcame the problem.

[howfar]

I've just tried the 22t on the original cranks giving 22-38-48 - there's a really poor shift onto the granny ring and it's almost impossible to shift back up - everything seems to be mangling!

I'll get a 24 & 26t inner on the original crankset with the original 113mm BB - that'll give me 24-38-48 or 26-38-48.

I know 28-38-48 works fine with Sora and 113mm BB - if the problem is with the inner ring being too small for the derailleur and FD cage radius wrong for the larger smaller crankset then I'll cheaply get nearer to the 20" gears.

Still yet to try the MTB mech from the commuter....

Thanks for your help everyone - much appreciated.